MKAbeFook for Facebook. Uses the WebKit browser with asynchronous requests, photo uploads, and much more. It can call any API method and returns the result in standard Cocoa types. It is distributed under a BSD style license.
Among the three largest social networking sites the most arcane to deal with from a developer perspective is LinkedIn. Now PeopleLinx is trying to prove there is a viable developer opportunity surrounding Linkedin APIs. The company, which just picked up an additional $3.2 million in financing, has developed an analytics application for LinkedIn that allows organizations to more easily ascertain what people are connected to what potential key accounts.